Infinitely variable friction gear

ABSTRACT

The infinitely variable friction wheel transmission with two transmission units and a traction element wound around the carriers of each respective transmission unit in the form of a Figure-8, comprises for each carrier a compensating element which exerts a restoring force on the carriers when a differential angle occurs between the two carriers.

[0001] The present invention concerns an infinitely variable frictionwheel transmission according to the pre-characterizing portion of claim1.

[0002] An infinitely variable friction wheel transmission of this typeusually has input and output discs arranged coaxially on a common shaft,arranged together in pairs and whose inside surfaces are designed intoroidal shape, with friction wheels arranged between the pairs of inputand output discs. These friction wheels are in frictional contact withboth the input discs and the output discs, and transfer the torque to betransmitted from the input disc to the output disc by virtue offriction-force contact, whre the rotation speed of the friction wheelsbeing the higher the larger is the distance between their point ofcontact with the input disc and the rotation axis. In contrast, therotation speed of the output discs is higher the closer the point ofcontact between the friction wheel and the output disc is to therotation axis. Accordingly, by swivelling the friction wheels, therotation speed of the output discs can be infinitely variably adjustedas desired. For this purpose, the rotation axles of the friction wheelsare in each case mounted on a carrier which can be controlled by meansof a swivelling device.

[0003] Such an infinitely variable friction wheel transmission isdescribed in detail in DE 197 54 725 by the present applicant. Thistransmission comprises two transmission units arranged coaxially withthe input shaft, each transmission unit having an input disc and anoutput disc between which, in each case, are arranged two frictionwheels, each friction wheel being attached on a carrier that can beswivelled. Both the input and the output discs are mounted on a torqueshaft which can be displaced slightly in the axial direction relative tothe input shaft. The input disc of one transmission unit is rotationallyfixed with respect to the torque shaft, but is mounted on the latter sothat it can slide axially on it. The input disc of the othertransmission unit too is connected to the torque shaft in a rotationallyfixed way by virtue of drive gearing. The two output discs of the twotransmission units are arranged mirror-symmetrically and adjacent to oneanother in the transmission, and are arranged on a common bushing, sothat a torque transmitted from one input disc to its associated outputdisc and a torque transmitted from the other input disc to itsassociated output disc, are transmitted from the two output discs inrotationally fixed connection with the bushing to a gear-wheel thatmeshes with a gearwheel of an output shaft. A roller-shaped pressingmechanism acts upon one of the input discs, which is mounted so as to bedisplaceable in the axial direction on the input shaft but is in arotationally fixed connection with it.

[0004] In the known infinitely variable friction wheel transmissions,the transmission ratio is usually adjusted by moving the friction wheelstangentially with respect to the transmission axle, such that, however,swivel forces from the input and output discs act on the friction wheelarranged between them, since to transfer the torque these discs have tobe pressed against the friction wheel. In conventional infinitelyvariable friction wheel transmissions the friction wheel in eachtransmission unit is arranged such that its swivel axis is positioned atthe mid-point of the torus formed by the associated input and outputdiscs. Thus, at the contact point of the friction wheel with itsassociated input and output discs, so-termed normal forces are producedwhen the transmission ratio is adjusted.

[0005] To avoid the possibility that the normal forces occurring duringtransmission ratio adjustment are unequal, the torque moment on thefriction wheel resulting from this might produce an undesired change ofthe transmission ratio of the transmission, it has already been proposedin DE 198 26 057 by the present applicant to compensate for a possibledifference in the normal forces by producing a control force, such thatwith the friction wheel held axially, this control force which leads totilting of the friction wheel, can be applied to one of the twoassociated discs, while when one of the discs is axially fixed, thecontrol force acts on the friction wheel.

[0006] It has also already been proposed to support the friction wheelsin an infinitely variable friction wheel transmission by means of twoconnecting rods which oppose the occurring reaction forces. In this, theswivelling movement of the friction wheels is made possible by rollerbearings; this design, however, has the disadvantage that the weight ofthe friction wheel transmission is higher and there is no coupling ofthe swivelling movements of two carriers arranged in a transmission unitfor the friction wheels.

[0007] Further, an infinitely variable friction wheel transmission hasbeen proposed, in which at the top and bottom ends of the carriers inany one transmission unit a traction element is provided, for example anendless cable, which passes around the corresponding ends of thecarriers essentially in a circle and which, to produce synchronousswivelling movements of the carriers in opposite directions, is arrangedin the form of a Figure-8, with a crossover point mid-way between thetwo carriers. This arrangement both takes up the reaction forces on thefriction wheels and also synchronizes the swivel angle of the twoassociated carriers in each transmission unit.

[0008] Now, if the traction element is used in such manner that nodifferential angle is possible between the carriers, i.e., the playbetween the traction element and the carrier is very small,manufacturing tolerances can lead to forced slippage under the frictionwheels. If the traction element is used such that there is large playbetween the traction element and the carrier, then the necessarycoupling between the carriers will only exist when there is already alarge differential angle between the two carriers.

[0009] The purpose of the present invention is to provide a couplingbetween the two carriers of any one transmission unit, which enables acertain, specified differential angle between the two carriers to be setbut, at the same time, when a differential angle occurs, a restoringforce on the corresponding carrier is produced.

[0010] This objective is achieved by the features indicated in claim 1;advantageous designs are described in the subordinate claims.

[0011] According to the invention, then, it is provided that acompensating element is associated with each carrier in a transmissionunit, which brings about effective coupling of the two carriers of thetransmission unit such that when a differential angle occurs between thetwo carriers, a restoring force is exerted on the carrier. Thecompensating elements are advantageously inserted as connection elementsin the traction element.

[0012] In an example of a preferred embodiment, the compensating elementcomprises a support disc in contact with a spring surrounded by asleeve, which is fitted so that it can move within a bushing against theforce of another spring, while the other section of the traction elementis attached to the center of the support disc.

[0013] The provision of a compensating element for each traction elementprovides the advantage that when a differential angle occurs, arestoring force is exerted on both carriers, whose effect is to reducethe differential angle. At the same time, tolerances in the mounting forthe traction element and in the traction element itself can becompensated by the gradual rise of the restoring force, without leadingto forced slippage at the contact points.

[0014] The manufacturing tolerances of the components, i.e., the holderfor the traction element and the traction element itself, can becorrespondingly greater. The behavior of the infinitely variablefriction wheel transmission can be affected by choosing differentcharacteristics for the springs used.

[0015] At the same time, the stability of the friction wheeltransmission is increased by this type of coupling; dampers provided inthe compensating element can damp any additional oscillations thatoccur.

[0016] Below, the invention is explained in more detail with referenceto the drawing in which two advantageous example embodiments areillustrated. The figures show:

[0017]FIG. 1 is a radial cross-section through a transmission unit of aninfinitely variable friction wheel transmission;

[0018]FIG. 2 is a schematic plan view of a traction element withinserted compensating element;

[0019]FIG. 3 is an enlarged representation of a compensating element;and

[0020]FIG. 4 is a partial representation of a traction element withanother example embodiment of a compensating element

[0021] Infinitely variable friction wheel variators are well known tothose familiar with the subject, so that in what follows, only thosecomponents necessary for understanding the invention are described andillustrated. The same components are denoted by the same referencenumbers in the various figures.

[0022] The two swivelling carriers for the friction wheels in atransmission unit are referenced as 1 and 2. A traction element indexed3 which, as viewed in FIG. 1, is provided at the bottom ends of the twocarriers 1, 2 for the friction wheels, wraps around the carriers 1, 2essentially in a circle, so that the two carriers 1, 2 are coupled inrelation to their swivel angle. For this, the traction element 3 isguided by holders 5 on the carriers 1, 2.

[0023] According to the invention, a so-termed phi-coupling is nowprovided between the two carriers 1, 2, in that two compensatingelements 4 are inserted in the traction element 3, such that a specifieddifferential angle between the two carriers 1, 2 can occur but, at thesame time, a restoring force is exerted on the carriers.

[0024]FIG. 3 shows a section through one of the compensating elements.When a differential angle (phi1-phi2) occurs, a support disc 9 ispressed against a spring 6 so as to produce a restoring force in thetraction element 3 on one of the two carriers 1, 2. By means of a seriesor parallel arrangement of various spring elements 6, 7 the restoringforce can be adjusted as a function of the differential angle and otherparameters.

[0025] The maximum permissible differential angle can be limited by asleeve. Advantageously, the restoring force on the carriers is small fora small differential angle, so that manufacturing tolerances will notresult in large restoring forces. In contrast, with larger differentialangles it is advantageous for the restoring force to increase steeply sothat if oscillations occur the effect of this phi-coupling is broughtinto play. Equally well, a damper can be integrated in the compensatingelement 4.

[0026] One end of the traction element 3 is connected to the supportdisc 9 by means of a locking disc 10, while the other end of thetraction element 3 is connected to the bushing 11 by means of a lockingdisc 10.

[0027] In the example embodiment of a compensating element shown in FIG.4, the holder for the traction element 3 is again referenced as 5; thecarrier 1 has a projection 14 which engages in a corresponding recesssuch that its rotation is limited by two abutments 12, 13. Two springs15, 16 are in each case attached at one end to the holder 5 for thetraction element 3 and are connected at the other end to the projection14 of the carrier 1. Here too, the size of the restoring force on thecarriers can be influenced by an appropriate choice of thecharacteristics of the springs. Reference numbers 1 Carrier 2 Carrier 3Traction element 4 Compensating element 5 Holder 6 Spring 7 Spring 8Sleeve 9 Support disc 10 Locking disc 11 Bushing 12 Abutment 13 Abutment14 Projection 15 Spring 16 Spring

1. Infinitely variable friction wheel transmission having at least twotransmission units, each transmission unit comprising an input discprovided coaxially with the input shaft and having a toroidally shapedinside surface, and an output disc arranged coaxially with the inputshaft and having a toroidally shaped inside surface, such that in eachcase an input disc and an output disc form a pair, several frictionwheels, which are arranged and are able to swivel between the pairs ofinput discs and output discs, and each of which is mounted on a carrier,for the transfer of a torque from the input disc to its associatedoutput disc by swivelling of the carriers and so too of the frictionwheels and a traction element which winds around the ends of thecarriers essentially in a circle and which, to produce a synchronousswivelling movement in opposite directions, is arranged in the form of afigure-8 with its crossover point mid-way between the two carriers,characterized in that with each carrier of a transmission unit there isassociated a compensating unit (4) which effectively couples the twocarriers (1, 2) of the transmission unit in such manner that when adifferential angle occurs between the two carriers, a restoring force isexerted upon the carriers.
 2. Infinitely variable friction wheeltransmission according to claim 1, characterized in that thecompensating elements (4) are inserted in the traction element (3) asconnection components.
 3. Infinitely variable friction wheeltransmission according to either of the preceding claims, characterizedin that each compensating element comprises a support disc (9) incontact with a spring (6) which is surrounded by a sleeve (8), saidsleeve being fitted in a bushing (11) so that it can be displacedagainst the force of another spring (7), and one section of the tractionelement (3) is attached centrally to the support disc (9) while theother end of the traction element (3) is attached to the end face of thebushing (11) facing towards the support disc (9).
 4. Infinitely variablefriction wheel transmission according to claim 1, characterized in thatthe compensating elements (4) are provided directly on the carriers (1,2).
 5. Infinitely variable friction wheel transmission according toclaim 4, characterized in that each compensating element comprises twosprings (15, 16), one end of each spring being attached to the holder(5) for the traction element (3) and the other end of each spring beingattached to a projection (14) of the carrier (1), and the projection(14) engages in a recess in the holder (5) and can swivel between twoabutments (13, 12) which delimit the recess.